Plant for pulverizing and burning coal



May 23, 1939.

a. GRAEMIGER PLANT FOE PULVERIZING AND BURNING COAL Filed Jan. 6, 1956EN AMIN v ESFQAEMIEEF? Patented May 23, 1939 UNITED STATES PATENT"OFFICE PLANT FOR PULVERIZING AND BURNING COAL Benjamin Graemiger,Zurich, Switzerland Application January 6, 1936, Serial No. 57,822 InSwitzerland January 8, 1935 3 Claims.

The invention relates to a method for operating pneumatic pulverizers inwhich the grinding operation is effected by a stream 01' gaseousoperating medium (as a rule air). The work pro-.

ducing stream is forms 9 by the-expansion of the I operating medium inone or more suitably shaped nozzles. The operating medium must becompressed and in most cases a heating also takes place after the,compression whereby the energy, thatis to say the velocity .of thestream, which is set free as -a result of the expansion is increased,When a predetermined energy of ex-' pension is. to be converted in thepulverizer the work of compression becomes the smaller the I higher thetemperature of the operating medium, ,whether a lower pressure isproduced or the quantity of operating-medium selected-is smaller.Heating operating mediumalso promotes the drying of the material tobe-ground which is generally damp, during the puverizing' operation andby the' drying the capacity of thematerial to grinding is also improvedin most cases, The heating of, the compressed operating medium isconsequently :2

advantageous for numerous reasons in most cases.

To the advantages of 'the pneumatic ,pulverizer, in connectionwith'which there istobe' particularly emphasized the omission of movableconstructional parts in the pulverizer itself, there is opposed in manycases and even when the heating of the operating medium'is carried to ,afarreaching extent, a high'requirement of energy for the compressionof'the gaseous operating medium as, compared with the requirement ofenergy by.

' pulverize'rs of a diflerent type.

The compression energy is taken up a motor which drives the compressor.inmost casesthis is an electric motor, occasionally also a steamturblue.t i

The invention has for its object to reducefthe cost for compressing theoperating mediumand,

thusfor the pulverizing; The invention'resides therein that into thegaseous operatingmedium, of which at .least one part serv'es'for theoperation of the pulverizer, there is' supplied, by compression andheating,,a larger amount of energy than is necessary for the operationof the pulverizer and that theexcess energy is utilized-in apower'engine which drives the compresson In this manner itbecomesipossible to carry out the compression work-necessary for theoperation: of

the pulveriz'er at least in part by heat supplied to the operatingvmedium and thus wholly or partly to effect an economy in the consumptionof mechanical or electrical energy. In most cases the price for heat andthe price for mechanical or electrical energy are inf'such a relationthat the expense involved for. the-pulverizing according to the methodaccording to the invention is consld-.

erably less than according tov one 'of [the methods hitherto-usual.Frequently also the heat which has been introduced may again be utilisedso that it is possible to effect a pulverizing which is practicallycostless;

The necessary excess of energy may be produced vinthat a. quantity ofoperating medium greater than that necessary for the operation of thepulverizer is compressed and heated and the. excess of operation mediumis expanded in a power engine which drives the compressor. This methodbecomes particularly advantageous when the Such a plant becomesparticularly simple .when l the whole of the combustion air is suppliedby the cpmpressor, of which one part serves as the operating air for thepulverizer and thus as the .3

primary air, and the other part after expansion has taken place as thesecondary air. A separate blower together with a' driving motor for thesecondary air then becomes unnecessary.

compressing the operating medium serving for the operation'of thepulverlzer to a pressure which is higher than thathecessary-foroperating .the pulverizer and after heating expanding it in a powerengineserving to drive the compressor, at least approximately to thepressure necessary'for operating the pulverizer. In this connection itmay occur that, the operating medium after expan'sion has taken place inthe power engine is still too hot to be capable of being used foroperatingthe pulverizerr In this case heat is withdrawn from theoperating medium before it heat in any suitable manner. This maypreferably be effected in that the withdrawn heat is supplied totheoperating-medium between the compressor and the power engine. i

In the/case. in which at'least apart of the :operating medium isseparated beyond the pulverizer, from the line material produced, in aseparator, this part may also be used for heating the operatingmediumbetween the compressor and the po'wer engine Naturally any otheruse ofthis .waste heat is possible, if desired also in There is then not onlysupplied The excess energy may also be obtained by entersthe'pulveriz'er, whilst naturally endeavours v are always made to againuse this-withdrawn heat still contained in the excess -of operating 1mediumafter expansion can be made capable grinding plant.

There may also be used a quantity of operating medium which is largerthan that necessary for the operation of the pulverizer and to compressthis to a pressure higher than that necessary for operating thepulverizer. The part of the operating medium necessary for the operationof the pulverizer then expands in the power engine driv-. ing thecompressor to the pressure necessary for the operation 'of thepulverizer, whilst the excess of operating medium expands in a powerengine to a pressure lower than that necessary for operating thepulverizer The expanded excess operating medium can then again be usedfor heating the operating medium between the compressor and the powerengine.

When the heat supplied to the system is not sufficient for obtaining theenergy for compression 0. motor can support the power engine in whichthe operating medium expands. It is particularly advantageous to includein the flow of the operating medium'an additional compressor which isthen in turn driven by a motor of any suitable type. Auxiliary energymay also be supplied to the system in that a compressed gaseous mediumof any suitable typeis introduced into the operating medium supplied bythe main compressor. This may be effected, for example, in that anauxiliary compressor driven in any suitable manner, operates in parallelwith the main compressor, or a medium, in 'vapdur form, under. pressureis supplied. The supply of such an additional medium may be effectedbefore or afterxheatingth'eoperating mediiun. Such an introduction ofadditional medium particularly arises during the period of starting sucha plant.

.power engine 4 (in which the operating medium expands). 5 is thepneumatic pulverizer to which the operating medium is supplied throughthe pipe l0, whilst the material to be pulverized is supplied throughthe pipe I5 and the dust produced flows ofi with the operating medium(expanded in the pulverizer) through the pipe [4. 1 is the suction pipeof the main compressor 3. In the admission pipe 9 of the expansion powerengine 4 is included the device for heating. the operating medium whichin Fig. l, is constructed as a surface heat exchanger ll, 12, whereasthe operating medium in the case of Fig.2 is heatedin. a combustionchamber 13 subjected to the pressure of the operating medium. In Fig. 2,there-is shown an auxiliary compressor 2, arranged in front of the maincompressor, and 6 is the suction pipe of the auxiliary compressor 2. InFig. 1 there is included in the pipe 8 also an additional heat exchangedevice [6, I1 through which the heat withdrawn from the expandedoperating material is conducted into the compressed operating medium.

As regards the diagrams the following may also be mentioned in detail byway of explanation. Assuming that the temperature of the operatingmedium, which flows through the pulverizer', may not be as high as thetemperature of the part which flows through the expansion power engine4, there is effected in Fig. 1 a branching of the pipe [0 between theheat exchanger l6, l1 and the heating device ll, i2. It is also possibleto branch the supply pipe to the pulverizer from an intermediate stageof the heat exchanger 1 I, I2 as is indicated in'Fig. 1 by the brokenline We. The coupling between the motor and the group,'consisting of thecompressor 3 and the power engine 4, may be effected directly or throughthe interposition of a transmission gear. The heating of the operatingmedium in the heat exchangers ll, l2 maybe effected, for example, by thewaste heat of a steam generator.

In Fig. 2, the heating of the operating medium is effected by thecombustion of any supply found in the combustion chamber i3 which isarranged between the pipes 8 and 9. 3| indicates the supply pipe for thefuel. In front of the combustion chamber a first portion of theoperating air is passed through the pipe 38 and behind the combustionchamber there is branched a second .portion" for the pulverizer throughthe pipe 39.

The two pipes are combined into the pipe Ill. In the pipe 38 is includeda regulating member 40 by which the temperature of the mixture in thepipe I0 can be influenced. The driving motor I is here not coupledmechanically to the group 34 but it drives the additional auxiliarycompressor 2. Such a compressor could also be included in the pressurepipe 8, further an additional compressor could be arranged in parallelwith the main compressor. By the pipe 4|, indicated in broken lines, isindicated an alternative by means of which an additional operatingmedium is supplied to the power engine 4. When for example 4 is a hotair turbine, then water vapour could be supplied through 4| forsupporting the operation by providing for this purpose an auxiliarynozzle. Such an auxiliary device may also be provided adjacent an actualdriving 'motor so as to provide supplementary means when starting orwhen the plant is subjected to an extremely high load. For the internalcombustion in the chamber 3, there may be selected a solid, liquid,gaseous, or mixed fuel. The heating may also be so effected that a firststage takes place by indirect heating (Fig. 1) and a second stage byinternal heating. The use of one part of the waste heat of the exhaustair of the power .engine 4 for heating the air in the pipe 8, maynaturally also be carried out within the scope of the diagram in Fig. 2.

For completing the explanation as to the method of operation in Figs..1and 2, there will be hereinafter set out numerically a first example. Ina furnace plant with direct blowing in of coal dust produced in apneumatic coal mill, the amount of coal dust produced and burnt isassumed to be 1 ton/hour. The energy to be applied between the expanslonnozzle and the dust air outfiowing from the mill is 24 kw. whichcorresponds with a coal capable of being ground moderately well. At atemperature in front of the nozzle of 250 C. and a pressure ratio of1.26 there is obtained a quantity of operating air of 2580 kg./hour. Thetotal quantity of air necessary for the combustion is 12900 kg./hour (10normal cubic meters/kg. coal). The compressor 3 supplies this totalquantity of air, having regard to the resistance in front of and behindthe mill at a; pressure ratio of 1.30. Assuming 20 C. in

the suctionpipe I, and a compression 'efiiciency adiabatic expansion of80% there is obtained an output of 115 kw. so that the driving motor isentirely unloaded. Without taking up external mechanical or electricalenergy, the grinding and conveying of the coal dust and in additionthedegree of pressure for overcoming the resistances are effected in theair heater and in the burner, The heat which is taken up is completelyutilized in the furnace .42 (having an outlet 43) both with the primaryair and also with the secondary air. This (in the case of the diagramFig. 2) has in the pipe 34 a temperature of 460 C. The primary airiscooled during the grinding operation only to such an extent as isnecessitated by the drying and heating of the coal. For both, however,it is no longer possible to supply the corresponding heat consumption inthe furnace. It is well known that the operation of coal-dust furnacesis promoted to a high degree by high temperatures of the; combustion airwhich is supplied. In the ease of a steam generator it is in generalalso very advantageous to mount in the system an air pre-heater assubsequent heating surface. Should the temperatures here assumed lead toundesirable conditions in the arrangement of the subsequent heatingsurfaces of the heat generator, then the upper stage of the heating canbe carried out separately either by an additional indirect heating or byinternal combustion.

Under usual conditions of operation'the compressor would bring 2580kg./hour operating air to the pressure ratio 1.30 and then take up anoutput of 27 kw. measured at the terminals of the ,driving electricmotor. desired to eflect an air preheating to the same extent, as occursin this example, there would also be the output of a secondary airblowenamounting to about 12 kw. The total gain thus amounts 'to about 39kw. In the present example there is assumed a single stage rotarycompressor and a single stage and single-bladed turbine.

In many cases, however, there exists between heat and current price aratio which is still more favorable for the method according to theinvention. This particularly occurs when the heat consumption can besupplied wholly or partly (particularly the low temperature sta'ges) .bywaste heat of any type; Particularly favorable is the case where theheat introduced into the system can be used in any way. This for exampleis the case when the air charged with fuel passing outthrough the pipeI4 is conducted into a furnace chamber. 7 I

The carrying out of the method leads in most cases to the use of asingle stage hot air turbine with a single or multi-stage compressor.These engine'"--'groups can be constructed in a particularlyadvantageous manner in that the suitable speed of rotation for theturbine and the compressor are well tuned to one another. There isconsequently obtained a minimum of weight and space requirement. This isparticularly the case when being used on vehicles of any kind ofimportance. The regulation of these groups is very satisfactory. Forinfluencing the operation there arise for example; The variation of thead- If, however, it is mission temperature of the turbine, the variation-of the nozzle cross section at the pulverizer, the

variation of any auxiliary energy that may be supplied.

The method according to the invention is in no way bound to the type ofengines which are used for compression and expansion. Also there is nolimitation to the selection of any auxiliary motor that may be requiredand in the method and manner of the introduction of the additionalenergy into the'system. The construction of the device for heating theoperating medium may have any imaginable forms. The pneumatic pulverizermay have any form of construction. The circuits and devices for the heattransmission may depart from the examples here shown. As regards thepressure and temperature between the total quantity of operating mediumand the part flowing to the pulverizer there is no limitation. Inparticular it is to be emphasized that also behind the pulverizer theremay obtain an appreciable pressure above atmospheric pressure, as -isfor example the case in connection with fuel pulverizing 'in combinationwith a furnace operating under pressure. There is no'restriction asregards either the' material to be pulverized or the gaseous operatingmedium to be used.

What I wish to secure by United States Letters Patent is:

1. A pulverizing plant which comprises in combination a compressorcompressing a gaseous operating medium, means for heating the compressedoperating medium, a power engine in which a part'of the compressed andheated operating medium expands and which drives said compressor, and apneumatic pulverizer in which the other part of the compressed and atleast in part heated operating medium expands, and

means for dividing the heated gas into two parts and for conducting onepart to the pulverizer and the other part to the engine.

2. A pulverizing plant which comprises in combination a compressorcompressing a gaseous operating medium, means for heating the compressedoperating medium, a power engine in which a part of the compressed andheated operating medium expands and which drives said compressor, apneumatic pulverizer in which the other part of the compressed andat'least in part heated operating medium expands, means for dividing theheated gas into two parts and for conducting one part to the pulverizerand the other part to the engine and means for transferring heatcontained in the part of the operating medium expanded in said powerengine into the operating medium leaving said compressor.

3. A plant for pulverizing and burning coal which comprises incombination a compressor compressing air, means for heating thecompressed air, a power engine in which a part of the compressed andheated air expands and which drives said compressor, a pneumatic coalpulverizer in which the other part 'of the compressed and fully orpartly heated air expands, means for dividing the heated gas into twoparts and for conducting one part to the pulverizer and the other partto the engine, a furnace,

means for blowing the air expanded in said' pulverizer as primary airtogether with the pulverized coal directly into said furnace, and meansfor blowing the air expanded in said power engine as secondary air intosaid furnace BENJAMIN GRAEMIGIR.

